Pressure intensifying apparatus for a die casting machine

ABSTRACT

A die casting machine for casting a molten metal in a mold includes a first piston-cylinder assembly which is operative to cause the molten metal to flow rapidly into the mold and a second piston-cylinder assembly which operates to apply an intensified fluid pressure on a piston surface of the first piston-cylinder assembly when the mold has been filled with the molten metal. The operation of both the first and second piston-cylinder assemblies may be selectively achieved by means of a control valve. The control valve has a piston located in a pressurized working fluid for causing the working fluid to move freely into the first piston-cylinder assembly to pour the molten metal rapidly into the mold during an initial casting process, but the same quickly closes an inlet of the working fluid to the first piston-cylinder assembly when a static pressure difference occurs between the front and rear surfaces of the piston of the control valve upon the mold becoming filled with molten metal, and then the control valve piston causes the working fluid pressure to effectively and quickly be applied on the functional surface of a piston of the second piston-cylinder assembly to generate the intensified pressure to be applied to the molten metal for making a uniform composition.

United States Patent [191 Mitamura et al.

May 8, 1973 [54] PRESSURE INTENSIFYING APPARATUS FOR A DIE CASTINGMACHINE [75] Inventors: Mitsuru Mitamura; Mamoru Ozeki,

both of Yokohama, Japan [73] Assignee: Toshiba Machine Co., Ltd., Tokyo,

Japan [22] Filed: Dec. 29, 1971 [211' Appl. No.: 213,629

[30] Foreign Application Priority Data Dec. 29, 1970 Japan ..45/130288[51] Int. Cl. ..B22d 17/32, B22c 19/04 [58] Field of Search ..164/303,312, 313,

[56] References Cited UNITED STATES PATENTS 2,228,973 l/l94l Polak..164/315 2,243,835 6/1941 Brunner.. ....l64/3l4 X 2,259,781 10/1941Shaw ....164/3l5 X 2,433,132 12/1947 Lester..... ....l64/3l4 X 2,484,90710/0949 Purcell ....l64/3l5 X 2,634,468 4/1953 Holder ..164/3l53,040,399 6/1962 Raffaelli ....l64/314 X 3,491,827 1/1970 Mace....l64/3l5 X 3,536,128 10/1970 Bachelier t ..l64/3l4 3,693,702 9/1972Piekenbrink ..l64/3l4 Primary Examiner-J. Spencer Overholser AssistantExaminer-John S. Brown Attorney-Norman F. Oblon et al.

[5 7 ABSTRACT A die casting machine for casting a molten metal in a moldincludes a first piston-cylinder assembly which is operative to causethe molten metal to flow rapidly into the mold and a secondpiston-cylinder assembly which operates to apply an intensified fluidpressure on a piston surface of the first piston-cylinder assembly whenthe mold has been filled with the molten metal. The operation of boththe first and second piston-cylinder assemblies may be selectivelyachieved by means of a control valve. The control valve has a pistonlocated in a pressurized working fluid for causing the working fluid tomove freely into the first piston-cylinder assembly to pour the moltenmetal rapidly into the mold during an initial casting process, but thesame quickly closes an inlet of the working fluid to the firstpiston-cylinder assembly when a static pressure difference occursbetween the front and rear surfaces of the piston of the control valveupon the mold becoming filled with molten metal, and then the controlvalve piston causes the working fluid pressure to effectively andquickly be applied on the functional surface of a piston of the secondpiston-cylinder assembly to generate the intensified pressure to beapplied to the molten metal for making a uniform composition.

9 Claims, 5 Drawing Figures Patented May" 8; 1973 4 Sheets-Sheet 1 FIG.6

Patented May 8, 1973 3,731,727

4 Sheets-Sheet l5 PRESSURE INTENSIFYING APPARATUS FOR A DIE CASTINGMACHINE BACKGROUND OF THE INVENTION 1. Field Of The Invention Thepresent invention relates generally to a pressure intensifying apparatusfor a die' casting machine and more particularly to such an apparatusfor obtaining a cast metal, such as aluminum, zinc, steel and the like,having a uniform composition.

2. Description Of The Prior Art As is well known in the art, in a diecasting process of a metal such as aluminum, zinc, steel and the like, amolten metal is first poured into a mold cavity of a die castingmachine, generally through operation of a pushing plunger, and then anintensified pressure is applied to the molten metal located within thecavity of the mold by the pushing plunger to make the composition of theresultant cast metal fine and uniform after the mold has been entirelyfilled with molten metal.

It is most important in such die casting processes to select the propertime at which the intensified pressure is to be applied to the moltenmetal that fills the cavity of the mold. If the intensified pressureoccurs at a delayed time after pouring the molten metal into the cavityof the mold, the inlet runner or passage of molten metal to the moldcavity may be stopped up by a part of solidified metal to therebyprevent further movement of the molten metal. As a result, theintensified pressure cannot be effectively transferred to the moltenmetal located in the mold cavity, and thus it is impossible to obtain acast metal product of high quality and having a fine and uniformcomposition.

Another problem is that unpreferable results also are obtained if anexcessive intensified pressure is applied to the molten metal in thecavity of the mold. This is usually caused by an abnormal function ofthe pressure control system for the pressure intensifying apparatus,such that a part of the molten metal is expelled from a joint portionbetween a movable die and a stationary die which cooperate to providethe mold of the die casting machine. Thus, casting fins may undesirablybe formed around the cast metal product, which must be removed therefromby expending much labor and time in order to obtain a cast product ofthe desired high quality. In addition to treating such a defect, anexcessive intensified pressure may also cause the mold to be broken.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an improved pressure intensifying apparatus for adie casting machine in which an intensifying pressure can be generatedat a desired time and without a time delay after filling the mold withmolten metal.

Another object of the present invention is to provide a pressureintensifying apparatus for a die casting machine in which an appropriateintensified pressure can be applied to a molten metal located within amold without danger of breaking the mold.

A further object of the invention is to provide a pressure intensifyingapparatus for a die casting machine capable of successfully obtainingcast products of high quality and uniform composition having no castingfins that must be removed therefrom.

The foregoing and other objects are attained, in accordance with thepresent invention, through the provision of a mold having a cavity formolding metal products therein comprising a pair of die members beingrelatively separable from each other. An injection sleeve having one endthereof in communication with the mold cavity is provided for injectingan amount of molten metal thereinto. The other end of the injectionsleeve has an opening for receiving molten metal and a pusher pistonslidably positioned therein for running the molten metal poured into thesleeve into the mold cavity through the one end thereof. There is alsoprovided a first piston-cylinder assembly having a first pistonconnected to the pusher piston of the injection sleeve through aconnecting rod member, the first piston being movable along the cylinderunder the pressure of a pressurized working fluid which may beselectively fed to the opposite functional surfaces of the first pistonfrom a pressurized fluid supply. In order to intensify the fluidpressure working on one surface of the first piston, there is provided asecond pistoncylinder assembly having a second piston slidablypositioned in the cylinder thereof, the second piston having a firstland portion of a large diameter and a second land portion of a smallerdiameter than the first land portion, both first and second landportions being integrally formed thereon, and the functional surface ofthe second land portion being in communication with one functionalsurface of the first piston to transfer an intensified fluid pressurefrom the former to the latter.

There is further provided a control valve means with a non-return valvemember, or check valve member, positioned in a pressurized fluidpassage, the check valve being operable for first supplying apressurized fluid to the first piston-cylinder assembly from apressurized fluid supply to move the first piston rapidly when the moldcavity is being filled with molten metal, and then for stopping the flowof pressurized fluid being supplied to the first piston-cylinderassembly in response to the presence of a static fluid pressuredifference between the opposite functional surfaces of the check valvewhich occurs when the first piston has stopped following the completionof the feeding of molten metal into the mold cavity.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features andattendant advantages will be more fully appreciated as the same becomebetter understood by reference to the following detaileddescription whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is an elevational sectional view, being partly broken away, ofthe mold of a die casting machine;

FIG. 2 is a schematic diagram of one embodiment of a pressureintensifying apparatus for a die casting machine formed in accordancewith the present invention;

FIG. 3 is a schematic diagram of another embodiment of a pressureintensifying apparatus formed in accordance with this invention;

FIG. 4 is a schematic diagram of a pressure intensifying apparatus ofstill another embodiment of the invention; and,

FIG. 5 is a schematic diagram of a pressure intensifying apparatus of astill further embodiment formed in accordance with the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring now to thedrawings, in which like reference numerals designate identical orcorresponding parts throughout the several figures, and particularly toFIG. 1 thereof, there is shown a die casting mold generally designatedby the reference numeral having a stationary die 11 and a movable die12. Dies 11 and 12 are provided with respective recesses on their facingsurfaces to form a mold cavity 13 into which molten metal may be poured.The movable-die 12 may be moved towards and 'away from the stationarydie 11 by any suitable mechanism of conventional design, not beingshown.

When the dies 1 l and 12 are closed for carrying out a molding process,a runner 14 is formed between the facing surfaces of the dies to run themolten metal into the cavity 13. In order to run the molten metal intothe cavity 13 through the runner 14, an opening 15 is provided throughthe stationary die 11 and a sleeve 16 for feeding molten metal throughthe opening 15 is also provided, as shown. At one end of the sleeve 16remote from the stationary die 11 is a radial opening 17 through whichan amount of molten metal 18 may be poured into the sleeve 16. The endof the sleeve 16 is closed by a pusher piston 19 slidably insertedtherein which is connected to one end of a piston rod 20 of a pressureintensifier, the description of which follows.

Reference is now made to FIG. 2, wherein a first piston-cylinderassembly generally designated by the reference numeral 21 is shownhaving a first piston 22 ofa relatively small diameter capable ofslidable movement along an inside wall of a first cylinder 23 and beingconnected to the other end of the connecting rod 20, which, ashereinbefore described, has one end connected to the pusher piston 19 ofFIG. 1. There is also provided a second piston-cylinder assemblygenerally designated by the reference numeral 24 having a secondcylinder 25 being larger in diameter than cylinder 23 and connectedthereto, and a second or stepped piston 32 having a land portion 26 ofasmaller diameter adapted for being slidably inserted in the firstcylinder 23 and a land portion 27 of a larger diameter adapted for beingslidably inserted in the second cylinder 25.

In order to supply a pressurized working fluid or oil into a chamber 28in the cylinder 23 being defined between a front surface 29 of the firstpiston 22 and the rear surface 30 of the smaller land portion 26 of thesecond piston 25, there is provided a through opening 31 axiallyextending through the second piston 32, into which a spool-like checkvalve 33 is slidably inserted. The check valve 33 comprises a tubularportion 34 at one end thereof, an elongate rod or stem 35 extending inone direction from a closed end of the tubular portion 34, and aterminating piston 36 on the other end of the rod 35 being slidablyenclosed in a cylinder 37 having one axial end attached to an axial endof the larger cylinder 25. The tubular portion 34 of check valve 33 alsohas at least one transverse through opening 38 near the closed or bottomend thereof, as shown. A

bore 39 with an internal diameter larger than the outer diameter oftubular portion 34 is provided in the second piston 32 being axiallyaligned with the opening 31 and having an axial length sufficient tocommunicate therethrough within the inside of tubular portion 34 overthe entire sliding stroke of the check valve 33.

The leftward position of the check valve 33, as viewed in FIG. 2, islimited by a stepped portion 40 provided in the opening 31. I

For supplying pressurized working oil,there is pro vided an oil pump 41to feed the oil from an oil tank or reservoir 42 into an accumulator 43,which is hereinafter called a pressurized oil supply. To selectivelydistribute the pressurized oil from the supply 43 thereof to the severalparts of the pressure intensifier, a three-position electromagneticcontrol valve 44 having first, second and third positions 45, 46-and 47is provided, being controlled through the selective energization anddeenergization of electromagnetic solenoid coils 48 and 49.

In the device of FIG. 2, the control valve 44 is shown occupying itsthird position 47 due to the energization of coil 49. In this position,pressurized oil fed from the accumulator 43 against the from functionalsurface of the second piston 32 in the large cylinder 25 through athrottle valve 50, a conduit 51, a passage 52 of the third position 47of control valve 44 and a conduit 53. Although the detail of the oilpassage will be further clarified later in the description, the oilreturn path may now be roughly traced from the leftward or rear chamber54 behind the first piston 22 in the first cylinder 23 through a conduit55, and through another passage 56 of the third position 47 of controlvalve 44 to the oil tank 42.

When the coils 48 and 49 are both deenergized, the control valve 44assumes its neutral or second position 46, in which the conduit 53 isconnected to the accumulator 43 through a throttle valve 57 of thesecond stage 46 having a smaller restricted section than that of thethrottle valve 50, and conduit is similarly connected through a passage58 of the second stage 46 to the tank 42. The first position 45 of thecontrol valve 44 will be assumed in place of the third stage 47 whencoil 48 is energized, and then a passage 59 will connect the accumulator43 to conduit 55 and a passage 60 will connect conduit 53 to the oiltank 42. This is used for the return movement of the pressureintensifier, the description of which follows.

In order to control the check valve 33, a second valve means 6, havingtwo stages or positions 62 and 63 and an oil pressure responsive valve64 are provided. The control valve 61 takes the first position 62 whenits electromagnetic solenoid coil 65 is deenergized, and takes itssecond position 63 when the same coil 65 is energized.

The pressure responsive valve 64 is located between conduits 55 and 66,and-one end of the latter conduit 66 opens into a chamber 67 which isdefined between the functional surface of the piston 36 and an end wallof the cylinder 37, as shown. The valve 64 has a pair of control inletsor conduits 68 and 69 for opening and closing the control thereof, beingof a conventional type, for example, with a pressure responsivediaphragm and a bias spring acting against the deviation of thediaphragm. If a higher pressure of oil exceeding a predeterminedamplitude acts upon the diaphragm through the conduit 69, the valve 64allows its passage 70 to communicate the conduit 55 with conduit 66. Onthe other hand, if a pressurized oil is conducted from conduit 55 intothe conduit 68, the valve 64 immediately opens the passage 70 to providecommunication between conduits 55 and 66 independently of thepredetermined pressure amplitude previously described.

When the valve 61 takes its first position 62, the passage 71 allows theconduit 69 to communicate with a chamber 72 being defined between thefront surface of the large piston 32 and an end wall of the cylinder 25,thereby causing the pressure responsive valve 64 to respond to the oilpressure in the chamber 72. If the second position 63 of control valve63 is assumed, its passage 73 makes conduit 66 communicate with chamber72 of the second piston-cylinder assembly 24 to thereby communicate thechamber 72 with chamber 67 in the cylinder 37, while passage 74 of thesecond position 63 causes the duct 69 to communicate with the oil tank42.

In order to obtain a desirable intensifying pressure, there are provideda first pressure-responsive valve, or first control valve, 75 and asecond pressure-responsive valve, or second control valve, 76 havingrespective passages 77 and 78 connected in series through a conduit 79.These valves 75 and 76 have similar construction to valve 64 describedabove. The inlet of the first valve 75 is connected to a chamber 80provided between a rear surface of the larger land 27 and the other endwall of the large cylinder 25. The outlet of the second valve 76 isconnected with the chamber 54 of the first piston-cylinder assembly 21.The first control valve 75 is controlled under a pressure of oil withinchamber 72 of the large cylinder 25, and responds to a predeterminedpressure value of the oil to open the passage 77 thereof. The secondcontrol valve 76 causes the section of passage 78 thereof to beregulated responsive to a predetermined pressure rise of oil in the duct79, and conducts the oil in chamber 80 into chamber 54. There is alsoprovided a check valve 81 across the pair of valves 75 and 76 such thatthe oil cannot flow therethrough in a leftward direction, as seen inFIG. 2, but the oil can flow easily therethrough in the rightwarddirection.

Prior to describing the operation of the device, let us assume thatchambers 28, 72, 80, 67 and other parts, with the exception of chamber54, are filled with oil, and check valve 33 is in the most leftwardposition being stopped by stepped portion 40 in the opening 31, whilevalves 64 and 75 close their passages 70 and 77, and control valve 61 isin the first position 62, as shown. Also assuming that dies 12 and 11have been closed and the piston 19 has been withdrawn to the mostrightward position in the sleeve 16 for the provision of die casting. Anamount of molten metal 18 is then poured into sleeve 16 through theopening 17. Both electromagnetic coils 48 and 49 of the control valve 44are deenergized in order to communicate passages 57 and 58 of the secondposition 46, thereof with conduits 53 and 55, respectively, as shown.

The pressurized oil from accumulator 43 is thus introduced into chamber72 through the throttle valve 50, conduit 51, throttle valve 57 having asection smaller than that of valve 50, and duct 53. Then the working oilenters freely into chamber 28 through openings 38 of the check valve 33being located at its open position and the opening 31 so that the firstpiston 22 will begin its movement slowly to the left along with thepusher rod 20. It will be easily understood that this slow forwardmovement of the piston 22 results from the smaller cross-section of thepassage 57 of the control valve 44.

Pusher rod 20 then drives the piston 19 slowly leftward to move themolten metal 18 towards runner l4 and then pours molten metal into thecavity 13. When the pusher rod 20 advances over a predetermineddistance, a limit switch, not shown, causes the coil 49 to be energizedso as to bring the third position 47 of the control valve 44 to itsfunctional position in place of the second position 46. Thus, thenarrower passage 57 is removed from the oil flow passage, and passage 52communicates duct 51 with duct 53 to feed a relatively larger amount ofworking oil from the accumulator 43 into the chamber 28 through throttlevalve 50, conduit 51, passage 52, duct 53, chamber 72, openings 38 ofthe check valve 33 and the opening 31. As a result, the first piston 22can be more quickly moved leftward along with its pusher rod 20 andpiston 19. The molten metal 18 will thus rush into the cavity 13 throughthe runner 14 to rapidly fill the cavity with molten metal.

It is understood, when pouring of molten metal into cavity 13 isintended, that the forward movement of piston 22 as described isentirely free, because the chamber 54 at the rear side of the piston 22is open to the tank 42 through conduit 55 and passage 58 or throughconduit 55 and passage 56.

When the cavity 13 in mold 10 is completely filled with molten metal 18,pistons 19 and 22 and the connecting pusher rod 20 will quickly come toa stop, and thereby oil pressure in the chambers 72, 28, opening 31 andbore 39 will suddenly increase.

In response to a predetermined amplitude of oil pressure rise in thechamber 72, pressure-responsive valve 64 allows its passage to be openedunder the oil pressure being transferred from chamber 72 into the valve64 through passage 71 of valve 61 and conduit 69. Thus, the chamber 67in front of piston 36 is brought into communication with tank 42 throughconduit 66, passage 70 of pressure-responsive valve 64, conduit 55 andpassage 5.6 of three-position valve 44, thereby allowing oil that hasfilled chamber 67 to be exhausted freely into the oil tank 42.

It will be clearly understood that the static oil pressures in chamber28, opening 31, bore 39 and chamber 72 will become equal anywhere toeach other immediately upon stopping the oil flow, as described above.Looking now at the closed or bottom portion of tubular portion 34 of thespool-like check valve 33, in which the front or rightward functionsurface has a pressure receiving area less than the rear or leftwardfunction surface of the bottom of the tubular portion 34 by an amountequal to the cross-section of stem 35, it is evident that a force willoccur operating to move the check valve 33 to the right, due to thedifference between these pressure-receiving areas.

The check valve 33 immediately moves rightward to close off the rightside opening of bore 39 with the bottom portion of tubular portion 34thereof. Thereafter, oil flow intended for entry into chamber 28 throughthe opening 31 will be effectively shut off. The oil pressure rise inchamber 72 is also immediately transferred to the firstpressure-responsive valve 75 causing it to open when the pressure riseovercomes the setting pressure amplitude. When the valve 75 opens, thepassage 77 communicates conduit 79 with the chamber 80 being definedaround land 26 of the stepped piston 32.

Thus the stepped piston 32 begins to move leftward under the increasedoil pressure in chamber 72, and at the same time the oil in chamber 80is pressed by the end wall of the land 27, increasing its pressure, andthis oil is then conducted into conduit 79 through the passage 77 of thecontrol valve 75. Thus, the second pressure-responsive valve or thesecond pressure-control valve 76 functions to regulate a cross sectionof its passage 78 to maintain the pressure of oil in chamber 80 at apredetermined level. The oil leaving valve 76 is then exhausted in oiltank 42 through chamber 54, conduit 55 and passage 56 of three-positioncontrol valve 44.

The stepped piston 32 can now be moved leftward responsive to a pressuredifference between chambers 72 and 80 to establish an intensified oilpressure in the chamber 28. This intensified oil pressure is added tothe function surface of the first piston 22, then is added to the moltenmetal filling the mold cavity 13 through the pusher rod 20 and piston 19so that the resultant cast product being obtained will possess a fineand uniform composition.

An examination of the prior art indicates that the most simpleconstruction of the check valve 33 would be a spool-like one with acoiled bias spring positioned in a tubular portion 34. These checkvalves were not provided with portions such as the stem 35 and piston36. The bias spring was provided with one end seated on stepped portion40 in the opening 31 and the other end seated on the bottom tubularportion 34 of check valve 33. It was found that it was very difficult todetermine the biasing force of the spring for the following reasons.

If the biasing force of the spring is made to be low, the pressurizedoil easily enters the chamber 28 by pushing the check valve forwardagainst the spring bias to push the first piston 22 forward with rod 20in a rapid manner, but once the piston 22 is stopped by filling of thecavity 13 with molten metal, the opening 31 is closed slowly due to theweak spring force. As a result, oil flow would continue through opening31 towards chamber 28, so that the time at which the pressureintensifying function by the second piston 32 occurs is unpreferablydelayed, whereby solidification of the molten metal 18 may occur at therunner 14 to prevent the intensified pressure being caused by the secondpiston-cylinder assembly 24 from being effectively transferred to themolten metal in the cavity 13. This obviously causes cast products to beproduced having rough and non-uniform composition.

In addition, there is another time delay inherent in the conventionaldie casting machines, which depends upon the amount of molten metal inthe cavity 13 and the compressibility thereof, the elasticcompressibility of the pusher rod 20, pistons 19, 22 and 32, and theworking oil as well. It can be seen that this time delay cannot beremoved because these factors are dependent on the size and material ofcasting products and the material to be used for manufacturing thevarious parts of the die casting machine. Accordingly, the aforesaidtime delay depending upon the spring coefficient of the check valve 33should be reduced to be as small as possible to emanate an intensifiedpressure increase at an appropriate time.

In order to reduce the time delay resulting from the use of aspring-biased check valve, consideration was given to increasing thestrength of the coiled spring. However, this method showed an undesiredresult in that the check valve 33 could not open the opening 31sufficiently to allow the oil flow to enter the chamber 28 easily whenthe rapid movement of the pusher rod 20 was required for pouring moltenmetal into the mold cavity 13. In this way the molten metal in cavity 13might be solidified before the intensified pressure rise took place.

In experiments conducted, there also sometimes occurred a wider openingof the passage 78 of the pressure-responsive valve 76 for the reason ofovershooting thereof. This was caused for the following reason. When acoiled biasing spring of weak strength was used in the tubular checkvalve 33 and an oil pressure rise occurred in chamber 28, if the checkvalve 33 could not simultaneously close the opening 31, the secondpiston 32 could go forward with a high speed since there was less loadon the second piston 32 due to the still open opening 31, such that anabnormal pressure rise might take place in chamber of the largercylinder 25 to cause the passage 78 of valve 76 to open widely,exceeding a desired sectional area. This might cause an excessiveintensified pressure to be added to the molten metal in mold cavity 13,and accordingly a part of the molten metal would be expelled out of thematched surfaces of the mold dies 11 and 12 to produce undesirable castfins on the product which in turn must be removed from the cast productsby expending much labor. Additionally, the mold 10 was apparentlyexposed to a danger of breakage due to the excessive intensifiedpressure. It was thus required to manufacture a very strong die castingmachine at high cost.

It will be easily understood from the previously described embodiment ofthis invention that the identified defects of the prior devices justdiscussed can be reduced satisfactorily by the present invention. Inother words, the die casting machine of this invention has nospring-biased check valve. The check valve 33 can be moved to close theopening 31 under a pressure difference that may be caused by adifference of size between front and back surfaces of a bottom portionof the tubular member 34 of check valve 33. The closing operation of thecheck valve 33 may occur at an earlier time or as soon as movement ofthe pusher rod 20 has been stopped due to the molten metal filling themold cavity 13. Actually, the check valve 33 closes communicationbetween the chambers 28 and 72 before the second piston 32 starts itsleftward movement for pressure-intensifying purposes. Thus, noovershooting of the pressure-responsive valve 76 may occur, and it ispossible to obtain the most preferable intensified pressure for applyingto the molten metal in the mold cavity 13 to manufacture cast productshaving fine and uniform composition and without having cast fins.

When the molten metal has been solidified in the mold cavity 13,solenoid coil 65 of the two-position control valve 61 is energized byany suitable timer relay, not shown, and the first position 62 is thenreplaced by the second position 63. In this way, passage 73 of secondposition 63 causes the chamber 72 to communicate with the chamber 67 ofcylinder 37 through passage 73 and conduit 66, and passage 74 releasesthe control oil of pressure-responsive valve 64 towards oil tank 42through conduit 69, to bring the passage 70 thereof to a closedposition. As a result, a pressurized oil is introduced from chamber 72into chamber 67 to advance the piston 36 forward along with tubularportion 34 and stem 35 of check valve 33 to reopen the opening 31 ofstepped piston 32. The pressurized oil from accumulator 43 is againsupplied into chamber 28 to advance the first piston 22 forward alongwith pusher rod 20 and piston 19, and accordingly solidified moltenmetal 18 left in the sleeve 16 is pushed out of the left end of thesleeve 16 when the movable die 12 is moved away from the stationary die11.

After the solidified metal is removed from the inside of sleeve 16, coil65 is deenergized to reset the control valve 61 to a position, as shown,and then solenoid coil 48 of the three-position control valve 44 isenergized. The first position 45 thus comes to its working position tocommunicate conduit 55 with accumulator 43 through passage 59 and tocommunicate conduit 53 with the oil tank 42 through passage 60. Thepressurized oil from accumulator 43 is supplied into chamber 54 throughthe passage 59 and conduit 55 and the oil in chamber 72 may be exhaustedtherefrom into the oil tank 42.

At the same time, the pressurized oil in conduit 55 is added to thepressureresponsive valve 64 through conduit 68 to communicate conduit 55with conduit 66 through passage 70 therein. In this case, the controlvalve 64 is so made that the passage 70 thereof is easily opened at alower pressure than that being received from conduit 69. This is easilyachieved by providing a larger pressure function area for oil to beentered through conduit 68 than that for oil from conduit 69.Accordingly, the pressurized oil from accumulator 43 is also suppliedinto chamber 67 to fill the same with oil so long as the conduit 55 isconnected to the accumulator 43. The check valve 33 is thus held in aposition such that the opening 31 is open to bore 39 through opening 38so that chambers 28 and 72 are communicated with each other freelythrough the opening 31.

The first piston 22 then moves to the right under the pressure of thepressurized oil being supplied to the chamber 54, and the oil in chamber28 is exhausted into tank 42 through opening 31 of stepped piston 32,openings 38 of the check valve 33, chamber 72 in cylinder 25, conduit 53and passage 60 of the threeposition control valve 44. The oil in chamber54 is also fed into chamber 80 around the smaller land portion 26 ofstepped piston 32 through check valve 81. Of course bothpressureresponsive valves 75 and 76 close their passages 77 and 78 atthis time. Thus the first piston 22 is returned towards its initialposition, and the stepped piston 32 is also returned rightward towardsits initial position.

All the parts of the die casting machine are therefore returned to theirinitial positions, respectively, and are ready for a succeeding diecasting operation.

FIG. 3 shows another embodiment of the invention that is nearly the sameas that of FIG. 2, except for an arrangement including a second controlvalve 83 and a check valve 84, replacing control valve 61. The secondcontrol valve 83 also has two stages or positions, the first beingdesignated by the numeral 85 and the second by 86, with the former one85 being as indicated when an electromagnetic solenoid coil 87 isdeenergized, and being replaced by the latter one 86 when the coil 87 isenergized. Check valve 84 is located between the conduits 66 and 88 sothat oil flow can take place only in a direction from conduit 88 toconduit 66.

Upon the quick feeding of the piston 22 together with its pusher rod 20for pouring molten metal into mold cavity 13, the control valve 83 takesits first posi' tion 85, as shown, to communicate chamber 72 of cylinder25 with conduit 69 through passage 89. In this case, passage 89 of thefirst position 85 of check valve 83 communicates conduit 88 with oiltank 42, but the check valve 84 does not allow oil flow to take placetherethrough. As described above, since chamber 67 is filled with oil toposition the spool-like check valve 33 at its most leftward position,pressurized oil from accumulator 43 is supplied into chamber 28 throughconduit 53, chamber 72 and opening 31 of the piston 32.

As in the first embodiment described before, oil flow directed fromchamber 72 to chamber 28 will stop suddenly as soon as the piston 22stops upon completion of pouring molten metal into the cavity 13,whereby the static oil pressure will increase in chambers 28 and 72 tomove the spool-like check valve 33 rapidly to the right to close theopening 31. This can be achieved by communication between conduits 66and 55 through the passage of the pressure-responsive valve 64 which inturn responds to the increased static pressure in chamber 72 throughpassage 89' and conduit 69.

In order to expel metal solidified in the sleeve 16 after solidificationof molten metal in the cavity 13, coil 87 is energized to change thevalve 83 from its first position to its second position 86. Thepressurized oil is then supplied from conduit 53 through passage 90 andcheck valve 84 into chamber 67 to move the spool like check valve 33leftward, and the same is freely flown into chamber 28 through chamber72 and opening 31 to move the first piston 22 leftward together with itspusher rod 20, while passage 91 releases the pressure applied on thecontrol valve 64 through conduit 69 and to the oil tank 42 to resetpassage 70 for shutting off communication between conduits 55 and 66.

FIG. 4 shows still another embodiment of the invention, in which aspool-like check valve assembly generally designated by a referencenumeral 93 has been taken outside of the stepped piston 32.

The check valve assembly 93 comprises a cylinder 94 having three tandemchambers 95, 96 and 97, a piston 98 slidably arranged in the chamber 95,another piston 99 slidably arranged in the chamber 97 and a connectingrod 100 connecting the pistons 98 and 99 to each other and extendingtherebetween. At the top of the cylinder 94, there is provided a furtherchamber 101 communicating with the chamber 28 of the firstpistoncylinder assembly 21 between the piston 22 and the piston 32through conduits 102 and 103, and the upper portion of piston 98 isslidably enclosed in the chamber 101. The chamber 95 has a valve seat104 on which the piston 98 can be seated or removed therefrom.

An eleetromagnetically operable two-position coritrol valve 105 isprovided, being similar to valve 61 of the embodiment shown in FIG. 2,and having a solenoid coil 106 and first and second positions 107 and108. The first position 107 of valve 105 has two passages 109 and 110,similarly the second position 108 has two passages 111 and 112, and thevalve takes a position as shown so long as the coil 106 is deenergized.When the coil 106 is energized, the first position 107 is replaced bythe second position 108 as the active position.

Chamber 95 is connected to a control inlet of pressure-responsive valve64 in a manner similar to that of the embodiment shown in FIG. 2 throughconduit 113, passage 110 of control valve 105 and conduit 69. Anothercontrol inlet for the valve 64 is connected to conduit 55 throughconduit 68 also in the same manner as that of FIG. 2. Chamber 96 ofcheck valve 93 is connected to the chamber 72 in front of the secondpiston 32 through conduit 114 and pressure-responsive valve 115. Thevalve 115 is controlled under the pressure of pressurized oil in chamber72 and communicates chamber 72 through passage 116 with conduit 114 soas to regulate the oil pressure in chamber 72 to a predeterminedamplitude. Chamber 96 of check valve 93 is also connected to conduit 53,which in turn is connected to the control valve 44 and related devicesas described by reference to FIG. 2.

In order to effect a forward feed of the first piston 22 along with itspusher rod for expelling the metal solidified in sleeve 16 of FIG. 1,there is provided an electromagnetically controllable valve 117 having apassage 118 which is brought to a position where conduit 66 iscommunicated with conduit 53 when a solenoid coil 119 is energized.

More particularly, in accordance with this embodiment, a pressurecontrol oil inlet of pressure-responsive control valve 75 is connectedto the chamber 28 in the first piston-cylinder assembly 21.

In operation, it is assumed that the chamber 97 in front of the piston99 of spool-like check valve 93 is filled with an amount of working oil,and piston 99 is pushed upward together with piston 98 and rod 100. Inthis way, pressurized oil from accumulator 43 is fed into chamber 28through conduit 102, chamber 95, valve seat 104, chamber 96, conduit 53and passage 52 of three-position valve 44 so that the piston 22 isadvanced forwardly along with rod 20 for feeding molten metal rapidlyinto the mold cavity 13.

When the mold cavity 13 has been filled with molten metal, the motion ofpiston 22 stops so that oil pressure in chamber 28 rapidly increases toa value substantially equal to that of accumulator 43. Oil flow stoppagealso occurs in chamber 95 and 96 of spool-like check valve 93 to developan equal static oil pressure on both end surfaces of piston 98.

Since the lower end surface of piston 98 has a smallerpressure-receiving area than the upper one thereof by an amount equal tothe cross-section of rod 100, the piston 98 is moved downward inresponse to the pressure difference thereon and is seated on the valveseat 104 to shut off the oil flow therethrough.

On the other the other hand, the pressurized oil in chamber 28 alsooperates on the pressure-responsive valve 64 through conduits 102 and113, passage 110 of valve 105 and conduit 69 to communicate the chamber97 below the piston 99 with conduit 55 through its passage 70 andconduit 66, so that oil in the chamber 97 is released to oil tank 42 toallow the downward movement of the piston 98.

Further, the increased oil pressure in chamber 28 operates onpressure-responsive valve through conduit 120 to allow the passage 77 tocommunicate chamber 80 in the cylinder 25 of the second pistoncylindercylinder assembly 24 with chamber 54 in cylinder 23 of the firstpiston-cylinder assembly 21, and then with oil tank 42 through conduit55 and passage 56 of the three-position control valve 44. Thus, thelarger piston 32 can be now moved leftward. At the same time, thepressurized oil is fed from accumulator 43 into chamber 72 in front ofthe piston 32 through throttle valve 50, passage 52 of valve 44,conduits 53 and 114 and passage 116 of pressure regulation valve 115.Thus, working oil regulated to a desired amplitude by the pressureregulation valve 115 is fed into chamber 72 so that the piston 32 canprovide a desired intensified oil pressure to be added to the moltenmetal in cavity 13, as described by reference to FIG. 2.

After solidification of the molten metal in the mold cavity 13, the mold10 is opened to take out the cast product, and then solenoid coil 119 ofcontrol valve 117 is energized to feed working oil from accumulator 43into chamber 97 below the piston 99 through passage 1 18 of the valve117. Thus the spoollike check valve 93 opens its valve seat 104 again tofeed working oil into chamber 28 through conduit 53, chambers 96 and andconduit 102, so that the piston 22 is advanced forwardly along withpusher rod 20 in order to remove the solidified metal from the sleeve16.

Next, coil 106 of control valve is energized to communicate the chamber95 of valve 93 with tank 42 through passage 112 to thereby discharge oilin the chamber 28 into oil tank 42, as well as to communicate conduit 69with tank 42 through passage 111 to reset the pressure-responsive valve64. Thus, the piston 22 can be moved freely to the right.

The coil 119 is deenergized, and then coil 48 of the three-positioncontrol valve 44 is energized so that the third position 47 of the valve44 is replaced by the first position 45 as the active position.Pressurized working oil is then fed from accumulator 43 into chamber 54through passage 59 and conduit 55. From conduit 55 a part of the workingoil is conducted to conduit 68 so that the passage 70 of valve 64 isactuated to allow conduits 66 and 55 to communicate with each other. Asa result, piston 99 again rises to remove piston 98 from its seat 104 sothat the oil in chamber 28 can be exhausted into tank 42 through conduit102, chambers 95 and 96 of valve 93, conduit 53 and passage 60 of thethree-position valve 44. Thus the piston 22 is returned rightwardtowards its initial position. A further part of the oil can be takenfrom chamber 54 into chamber 80 through check valve 81 so that thestepped piston 32 is returned towards its rightward initial position.

All the parts of the die casting machine are thus returned to theirinitial positions for permitting a succeeding die casting process to becarried out.

It can be seen that the same objects and features as those of FIGS. 2and 3 can be achieved by the embodiment described by reference to FIG.4. Additionally, since the spool-like check valve 93 is located outsidethe stepped piston 32, manufacture of the stepped piston 32 and thecheck valve 93 is made much easier without requiring alignment of theparts.

FIG. shows a still further embodiment of the invention, in which thefirst piston-cylinder assembly 21 and the second piston-cylinderassembly 24 are made separately and are connected to each other througha conduit 121, as shown. In accordance with this arrangement, thepiston-cylinder assembly 24 can be located freely at a position remotefrom the first assembly 21 so that there may be obtained much morefreedom in the manufacture and building of the die casting machine.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent oftheUnited States is:

1. Pressure intensifying apparatus for a die casting machine comprising:

A mold having relatively separable dies facing each other and defining amold cavity therebetween for receiving molten metal for making a castproduct;

a sleeve member having one end thereof connected to said mold forfeeding an amount of molten metal into said cavity;

a first piston-cylinder assembly having a first cylinder slidablyreceiving a first piston, another piston slidably disposed in saidsleeve for forcing molten metal therefrom and into said mold cavity, anda pusher rod having one end connected to the first piston and extendingfrom one end of the first cylinder and its other end connected to saidanother piston in said sleeve;

a second piston-cylinder assembly having a second piston and a secondcylinder slidably receiving said second piston, said second piston beingformed with a first land portion and a second land portion of greaterdiameter than the first land portion and said second cylinder beingprovided with a first portion substantially equal in diameter to saidfirst land portion being slidably disposed therein and a second portionsubstantially equal in diameter to said second land portion beingslidably disposed therein and a chamber in said first portion of saidsecond cylinder on one side of said first land portion being open tosaid first cylinder on the first piston side thereof so as to enable afluid pressure to be transmitted from said chamber of said secondcylinder onto a functional surface of said first piston;

means for feeding a working fluid into first cylinder on the firstpiston side thereof comprising a spoollike check valve member positionedin said working fluid to allow said working fluid to flow into saidfirst cylinder to move said first piston so as to feed molten metal intothe mold cavity, said check valve including axially opposed end surfaceshaving different pressure-receiving surface areas so that the checkvalve shuts off the feeding of working fluid into said first piston sideof said first cylinder in response to a sudden increase in pressure ofthe working fluid therein which occurs when the movement of said firstpiston has been stopped by the filling of said mold cavity with moltenmetal; and,

means for applying a regulated fluid pressure on the functional surfacesof said second land portion of said second piston to remove a desiredintensified pressure from the second piston when said spoollike checkvalve shuts off working fluid flowing into the first piston side of saidfirst cylinder.

2. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein:

said second piston of second piston-cylinder assembly is provided withan axially extending through opening for flowing a working fluidtherethrough and a bore provided at an intermediate position along thelongitudinal axis of the opening, said bore having a larger internaldiameter than that of the opening; and,

said spool-like check valve includes a tubular portion slidably locatedin said through opening having an open end facing towards the functionalsurface of said first piston, a closed bottom opposite said open end,and at least one radial opening through which the working fluid canflow, a stern member extending from the bottom of said tubular portionlongitudinally through said through opening and end wall of secondcylinder of said second pistoncylinder assembly, and a piston mounted onthe end of said stern being slidably received in an additional cylindermounted on said end wall of said second piston-cylinder assembly,

said spool-like check valve being capable of movement along said throughopening by a defined stroke so that said radial opening of the tubularportion thereof is always exposed in said bore over the entire stroke ofsaid check valve, one of the axially opposite surfaces of said bottom ofthe tubular portion having a larger pressure-receiving surface area thanthe other surface by an amount equal to the cross-section of said stemso that a pressure difference resulting therefrom causes said checkvalve to close said through opening in a direction depending upon thepressure difference when a static fluid pressure is developed on thebottom, and said piston being mounted on the end of saidstem causingsaid bottom of said tubular portion to move away from its closed portionto open said through opening when a working fluid is supplied onto thefunctional surface thereof in said additional cylinder.

3. Pressure intensifying apparatus for a die casting machine accordingto claim 1, further comprising:

a spring-biased fluid back pressure control valve connected in serieswith a passage for exhausting fluid from a chamber defined by a steppedportion of said second piston between said land portions and said secondcylinder so that a predetermined intensified fluid pressure can beprovided by said second piston-cylinder assembly.

4. Pressure intensifying apparatus for a die casting machine accordingto claim 2, further comprising:

a pressure-responsive valve connected with said second cylinder and saidadditional cylinder and being responsive to a sudden increase inpressure of the working fluid in a chamber in front of said secondpiston so that a working fluid filling a chamber in front of said pistonin said additional cylinder may be exhausted from the additionalcylinder to allow movement of the piston therein to close said throughopening in said second piston.

5. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein:

said first cylinder of said first piston-cylinder assembly has its oneopen end directly connected to an open end of said second cylinder ofsaid second piston-cylinder assembly, and the open end of said firstcylinder is provided with a portion having a diameter substantiallyequal to that of said first land portion of the second piston forslidably receiving the same.

6. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein said spool-like check valve member comprises:

a cylinder having first, second, third and fourth chambers arranged intandem therein, the second chamber having an opening with a valve seatfor fluidly connecting the second chamber with the third chambertherethrough, and first and second pistons connected to each otherthrough a piston rod, a part of said first piston being slidablyreceived in said first chamber, said first piston being also providedwith opposing first and second.

fluid function surfaces, the second surface having a smaller area thatthe first surface by an amount substantially equal to the cross-sectionarea of said piston rod and a shape suitable for seating on said valveseat of the second chamber to shut off said opening against fluid flowtherethrough; and,

said first and second chambers are communicated with a chamber in frontof said first piston of said first piston-cylinder assembly, said thirdchamber is connected to a pressurized fluid supply, and said fourthchamber may be connected to the fluid supply when required for causingsaid first piston of said check valve to open said valve seat and isreleased when a pressurized fluid is supplied from the supply to saidthird chamber.

7. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein:

said second piston of said piston-cylinder assembly is of solidconstruction, said spool-like check valve member is located outside ofsaid second piston, and a pressure control valve is positioned in anupward stream of the working fluid that flows into a chamber of thesecond cylinder in front of said second piston to thereby generate adesirable intensified pressure from said second piston-cylinder assemblyin response to the pressure of the working fluid in said chamber.

8. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein:

said first and second piston-cylinder assemblies are spaced apart andare connected through conduit means for transferring an intensifiedfluid pressure from the second piston-cylinder assembly to the firstpiston-cylinder assembly.

9. Pressure intensifying apparatus for a die casting machine comprising:

a mold having relatively separable dies facing each other and defining amold cavity therebetween for receiving molten metal for makin a castproduct; a sleeve member having one end t ereof connected to said moldfor feeding an amount of molten metal into said cavity;

first piston transfer means having a part thereof slidably disposed insaid sleeve for feeding said molten metal therefrom and into saidcavity;

second piston transfer means for supplying fluid under pressure to saidfirst piston transfer means for moving the same in one direction;

a spool-like check valvemember in said second piston transfer means forselectively permitting flow therethrough and preventing fluid flowtherethrough; and,

fluid flow control means for positioning said check valve to permitfluid flow therethrough to operate said first piston transfer means andupon filling said mold cavity being responsive for positioning saidcheck valve to prevent further flow through said second piston transfermeans, and further for subsequently operating said second pistontransfer means to intensify the pressure of said fluid acting upon saidfirst piston transfer means.

1. Pressure intensifying apparatus for a die casting machine comprising:A mold having relatively separable dies facing each other and defining amold cavity therebetween for receiving molten metal for making a castproduct; a sleeve member having one end thereof connected to said moldfor feeding an amount of molten metal into said cavity; a firstpiston-cylinder assembly having a first cylinder slidably receiving afirst piston, another piston slidably disposed in said sleeve forforcing molten metal therefrom and into said mold cavity, and a pusherrod having one end connected to the first piston and extending from oneend of the first cylinder and its other end connected to said anotherpiston in said sleeve; a second piston-cylinder assembly having a secondpiston and a second cylinder slidably receiving said second piston, saidsecond piston being formed with a first land portion and a second landportion of greater diameter than the first land portion and said secondcylinder being provided with a first portion substantially equal indiameter to said first land portion being slidably disposed therein anda second portion substantially equal in diameter to said second landportion being slidably disposed therein and a chamber in said firstportion of said second cylinder on one side of said first land portionbeing open to said first cylinder on the first piston side thereof so asto enable a fluid pressure to be transmitted from said chamber of saidsecond cylinder onto a functional surface of said first piston; meansfor feeding a working fluid into first cylinder on the first piston sidethereof comprising a spool-like check valve member positioned in saidworking fluid to allow said working fluid to flow into said firstcylinder to move said first piston so as to feed molten metal into themold cavity, said check valve including axially opposed end surfaceshaving different pressure-receiving surface areas so that the checkvalve shuts off the feeding of working fluid into said first piston sideof said first cylinder in response to a sudden increase in pressure ofthe working fluid therein which occurs when the movement of said firstpiston has been stopped by the filling of said mold cavity with moltenmetal; and, means for applying a regulated fluid pressure on thefunctional surfaces of said second land portion of said second piston toremove a desired intensified pressure from the second piston when saidspool-like check valve shuts off working fluid flowing into the firstpiston side of said first cylinder.
 2. Pressure intensifying apparatusfor a die casting machine according to claim 1, wherein: said secondpiston of second piston-cylinder assembly is provided with an axiallyextending through opening for flowing a working fluid therethrough and abore provided at an intermediate position along the longitudinal axis ofthe opening, said bore having a larger internal diameter than that ofthe opening; and, said spool-like check valve includes a tubular portionslidably located in said through opening having an open end facingtowards the functional surface of said first piston, a closed bottomopposite said open end, and at least one radial opening through whichthe working fluid can flow, a stem member extending from the bottom ofsaid tubular portion longitudinally through said through opening and endwall of second cylinder of said second piston-cylinder assembly, and apiston mounted on the end of said stem being slidably received in anadditional cylinder mounted on said end wall of said secondpiston-cylinder assembly, said spool-like check valve being capable ofmovement along said through opening by a defined stroke so that saidradial opening of the tubular portion thereof is always exposed in saidbore over the entire stroke of said check valve, one of the axiallyopposite surfaces of said bottom of the tubular portion having a largerpressure-receiving surface area than the other surface by an amountequal to the cross-section of said stem so that a pressure differenceresulting therefrom causes said check valve to close said throughopening in a direction depending upon the pressure difference when astatic fluid pressure is developed on the bottom, and said piston beingmounted on the end of said stem causing said bottom of said tubularportion to move away from its closed portion to open said throughopening when a working fluid is supplied onto the functional surfacethereof in said additional cylinder.
 3. Pressure intensifying apparatusfor a die casting machine according to claim 1, further compriSing: aspring-biased fluid back pressure control valve connected in series witha passage for exhausting fluid from a chamber defined by a steppedportion of said second piston between said land portions and said secondcylinder so that a predetermined intensified fluid pressure can beprovided by said second piston-cylinder assembly.
 4. Pressureintensifying apparatus for a die casting machine according to claim 2,further comprising: a pressure-responsive valve connected with saidsecond cylinder and said additional cylinder and being responsive to asudden increase in pressure of the working fluid in a chamber in frontof said second piston so that a working fluid filling a chamber in frontof said piston in said additional cylinder may be exhausted from theadditional cylinder to allow movement of the piston therein to closesaid through opening in said second piston.
 5. Pressure intensifyingapparatus for a die casting machine according to claim 1, wherein: saidfirst cylinder of said first piston-cylinder assembly has its one openend directly connected to an open end of said second cylinder of saidsecond piston-cylinder assembly, and the open end of said first cylinderis provided with a portion having a diameter substantially equal to thatof said first land portion of the second piston for slidably receivingthe same.
 6. Pressure intensifying apparatus for a die casting machineaccording to claim 1, wherein said spool-like check valve membercomprises: a cylinder having first, second, third and fourth chambersarranged in tandem therein, the second chamber having an opening with avalve seat for fluidly connecting the second chamber with the thirdchamber therethrough, and first and second pistons connected to eachother through a piston rod, a part of said first piston being slidablyreceived in said first chamber, said first piston being also providedwith opposing first and second fluid function surfaces, the secondsurface having a smaller area that the first surface by an amountsubstantially equal to the cross-section area of said piston rod and ashape suitable for seating on said valve seat of the second chamber toshut off said opening against fluid flow therethrough; and, said firstand second chambers are communicated with a chamber in front of saidfirst piston of said first piston-cylinder assembly, said third chamberis connected to a pressurized fluid supply, and said fourth chamber maybe connected to the fluid supply when required for causing said firstpiston of said check valve to open said valve seat and is released whena pressurized fluid is supplied from the supply to said third chamber.7. Pressure intensifying apparatus for a die casting machine accordingto claim 1, wherein: said second piston of said piston-cylinder assemblyis of solid construction, said spool-like check valve member is locatedoutside of said second piston, and a pressure control valve ispositioned in an upward stream of the working fluid that flows into achamber of the second cylinder in front of said second piston to therebygenerate a desirable intensified pressure from said secondpiston-cylinder assembly in response to the pressure of the workingfluid in said chamber.
 8. Pressure intensifying apparatus for a diecasting machine according to claim 1, wherein: said first and secondpiston-cylinder assemblies are spaced apart and are connected throughconduit means for transferring an intensified fluid pressure from thesecond piston-cylinder assembly to the first piston-cylinder assembly.9. Pressure intensifying apparatus for a die casting machine comprising:a mold having relatively separable dies facing each other and defining amold cavity therebetween for receiving molten metal for making a castproduct; a sleeve member having one end thereof connected to said moldfor feeding an amount of molten metal into said cavity; first pistontransfer means having a part thereof slidably disposed in said sleevefor feeding said molten metal therefrom and into said cavity; secondpiston transfer means for supplying fluid under pressure to said firstpiston transfer means for moving the same in one direction; a spool-likecheck valve member in said second piston transfer means for selectivelypermitting flow therethrough and preventing fluid flow therethrough;and, fluid flow control means for positioning said check valve to permitfluid flow therethrough to operate said first piston transfer means andupon filling said mold cavity being responsive for positioning saidcheck valve to prevent further flow through said second piston transfermeans, and further for subsequently operating said second pistontransfer means to intensify the pressure of said fluid acting upon saidfirst piston transfer means.